1. Field of the Invention
The present invention relates to an electrostatic reproducing apparatus in which an equipotential surface is established between an ion generator and an ion modulating electrode to condense the ion flow and to increase its density, and the ion flow passing through said ion modulating electrode is improved.
2. Description of the Prior Art
Electrostatic reproducing apparatus of a variety of types have now been proposed to record onto a recording paper the image signal produced by the computer, the image signal transmitted over communication lines, and image signal obtained by converting original image into electric signals by solid stage image sensors such as CCD (Charge Coupled Device image sensor). In an electrostatic reproducing apparatus, an electrostatic latent image corresponding to an image signal is formed on a charge receptor such as photosensitive material, dielectric material and electrostatic recording paper. As a means for forming the electrostatic latent image, there is an electrostatic reproducing apparatus of the type in which electrostatic latent image is formed on a dielectric material by utilizing an ion modulating electrode which modulates corona ions produced by a corona wire or the like corresponding to image signals. FIG. 1 schematically illustrates an electrostatic reproducing apparatus of this type, according to which image signals obtained by photoelectrically converting an original image by the solid state image sensors such as CCD or electric image signals from a computer or transmitted over communication lines, are fed to a signal processing circuit 1, and the processed image signal are fed to a circuit 2 for driving an ion modulating electrode 4. Reference numeral 3 denotes a control circuit including a clock generator which provides timing for applying signals from the signal processing circuit 1 to the drive circuit 2. The ion modulating electrode 4 consists of an insulating layer coated on each side with a continuous layer 4a of a conductive material and a segmented layer 4b of a conductive material, and has a plurality of apertures 4c that are formed in a single row or in a plurality of rows. The segmented layer 4b of a conductive material is applied with image signals from the drive circuit 2. A corona ion generator 5 including a corona wire 5a is disposed above the ion modulating electrode 4, and a rotary drum 6 made of a dielectric material is located under the ion modulating electrode 4. Around the periphery of the dielectric rotary drum 6 are provided a developing device 7, a transfer electrode 8, a separating pawl 9, a charge eliminating electrode 10, and a cleaning blade 11, that are necessary for ordinary electrophotographic process. There is also provided a fixing device 12. The ions generated from the corona ion generator 5 pass through the apertures 4c being controlled by control signals applied to the segmented layer 4b of the ion modulating electrode 4. Therefore, an electrostatic latent image corresponding to the original image signal that are to be reproduced is formed on the dielectric material of the rotary drum 6. The thus formed electrostatic latent image is developed by a developer in the developing device 7, and is transferred onto the recording paper P by the transfer electrode 8. Thereafter, the recording paper P is separated from the dielectric rotary drum 6 by the separating pawl 9, and is ejected out of the apparatus after the toner image has been fixed by the fixing device 12.
The electrostatic reproducing method employing the ion modulating electrode is capable of reproducing images of a high quality having excellent resolution and toner reproduction, maintaining the electrode and the electrostatic image-forming member such as dielectric member apart (0.1 to 2.0 mm). This method, however, presents the problem that the recording speed is low because (1) there is a limit in the current density of corona ion generated by the ion generator (about 10 .mu.A/cm.sup.2), and (2) there is a lower limit in the ion control time due to the mobility of ions. Therefore, the above-mentioned method had been used simply for a printer utilizing ink mist (e.g. U.S. Pat. No. 3,779,166). Accordingly, the electrostatic reproducing system of the present time chiefly employs a multistylus electrode. In order to increase the recording speed in the electrostatic reproducing method employing and ion modulating electrode, therefore, there can be proposed a method of using an ion generating source (utilizing, for example, a high-frequency discharge or a spark discharge) as a substitute for the ion generator which employs the corona wire, resulting, however, in a complicated construction as compared with the apparatus using the corona wire.
FIG. 2 shows the ion flow by the conventional ion modulating electrode, in which solid lines represent equipotential surfaces, and broken lines represent ion flow path. The ion stream generated by the corona wire 5a flows toward the ion modulating electrode 4 according to the equipotential surface established by the potential difference between the corona wire 5a and the continuous layer 4a, and enters into the apertures 4c. In order to increase the proportion of ions that enter into the apertures 4c, the potential difference between the continuous layer and the segmented layer is increased. Then, the equipotential surface is established as indicated by solid lines in FIG. 2, the ion flow paths are also established as indicated by broken lines. If the potential difference is decreased, the amount of ions that enter is reduced, and the amount of ions that pass through is reduced. In order to increase the recording speed, therefore, the potential difference must be increased between the continuous layer of a conductive material and the segmented layer of a conductive material. In this case, portions of the ion flow entering the apertures 4c may adhere onto the insulation layer between the continuous layer 4a and the segmented layer 4b, and another portion of the ion flow may be attracted by the segmented layer 4b, so that the passing ratio of ion flow decreases to less than 10%. Here, the ion flow passing ratio stands for a ratio of an electric current by the ion flow that passes through the apertures 4c to an electric current by the ion flow that enter into the apertures 4c of the ion modulating electrode.